1. Field of the Invention
The present invention relates to an active-matrix display apparatus including pixel display elements (each also referred to as a pixel electro-optical device) arranged to form a matrix in a display area and relates to a pixel electric-potential correction method.
2. Description of the Related Art
Typical display apparatus include a liquid-crystal display apparatus typically employing pixel circuits each including a liquid-crystal cell functioning as a display element also referred to as an electro-optical device. The liquid-crystal display apparatus is characterized in that the apparatus is thin and has a low power consumption. The liquid-crystal display apparatus is used as a display unit in a wide range of electronic equipment such as a personal digital assistant (PDA), a hand-held phone, a digital camera, a video camera and a personal computer.
FIG. 15 is a diagram roughly showing a typical configuration of an existing liquid-crystal display apparatus 1. For more information on this liquid-crystal display apparatus 1, the reader is suggested to refer to Patent Documents 1 and 2 (Japanese Patent Laid-open No. Hei 11-119746 and Japanese Patent laid-Open No. 2000-298459 (hereinafter referred to as Patent Document. 1 and 2)). As shown in FIG. 15, the liquid-crystal display apparatus 1 employs an available pixel section 2, a vertical driving circuit (VDRV) 3 and a horizontal driving circuit (HDRV) 4 which are provided on the peripheries of the available pixel section 2.
In the available pixel section 2, a plurality of pixel circuits 21 are arranged to form a matrix. Each of the pixel circuits 21 includes a thin-film transistor TFT21 functioning as a switching device, a liquid-crystal cell LC21 and a storage capacitor CS21. The TFT is an abbreviation for the thin-film transistor. The first pixel electrode of the liquid-crystal cell LC21 is connected to the drain electrode (or the source electrode) of the thin-film transistor TFT21. The drain electrode of the thin-film transistor TFT21 is also connected to the one of electrodes of the storage capacitor CS21.
Scan lines (or gate lines) 5-1 to 5-m are each provided for a row of the matrix. The scan lines 5-1 to 5-m are arranged in the column direction. Signal lines 6-1 to 6-n arranged in the row direction are each provided for a column of the matrix.
As described above, the gate electrodes of the thin-film transistors TFT21 employed in the pixel circuits 21 provided on a row are connected to a scan line (one of the scan lines 5-1 to 5-m) provided for the row. On the other hand, the source (or drain) electrodes of the thin-film transistors TFT21 employed in the pixel circuits 21 provided on a column are connected to a signal line (one of the signal lines 6-1 to 6-n) provided for the column.
In addition, in the case of an ordinary liquid-crystal display apparatus, a storage-capacitor line Cs is provided separately. The storage capacitor CS21 is connected between the storage-capacitor line Cs and the first electrode of the liquid-crystal cell LC21. Pulses having the same phase as a common voltage Vcom are applied to the storage-capacitor line Cs. In addition, the storage capacitor CS21 of every pixel circuit 21 on the available pixel section 2 is connected to the storage-capacitor line Cs serving as a line common to all the storage capacitors Cs21.
On the other hand, the second pixel electrode of the liquid-crystal cell LC21 of every pixel circuit 21 is connected to a supply line 7. The supply line 7 provides the common voltage Vcom, which is a series of pulses with a polarity typically changing once every horizontal scan period. One horizontal scan period is referred to as 1H.
FIGS. 16A to 16E show timing charts of the so-called 1H Vcom inversion driving method of the ordinary liquid-crystal display apparatus shown in FIG. 15.
Incidentally, a capacitive coupling driving method has the following problems. If a liquid-crystal material exhibiting the characteristic of the liquid-crystal dielectric constant ∈ to an applied voltage is used in a liquid-crystal display apparatus, a luminance change observed at a manufacturing time as a luminance change in a liquid crystal gap is seen to have a big value, causing a problem in consideration of an effective pixel electric potential. An example of the liquid crystal material exhibiting the characteristic of the liquid crystal dielectric constant ∈ to an applied voltage is the normally white liquid crystal.
In addition, an effort to optimize the black luminance faces a problem of the white luminance becoming black, that is, a problem of the white luminance sinking.
In order to solve the problems of the capacitive coupling driving method, a display apparatus disclosed in Japanese patent Laid-Open No. 2007-65076 is provided. The display apparatus employs a correction circuit system for correcting the dynamic range of an available pixel section of the display apparatus. The display apparatus employing the existing correction circuit system is explained by referring to FIGS. 17 and 18. FIG. 17 is a block diagram showing the display apparatus.
The display apparatus shown in FIG. 17 employs an available pixel section 34, a monitor pixel section 35 and a correction circuit 30. The available pixel section 34 is a section serving as the actual display surface. The monitor pixel section 35 is a section having a configuration identical with the configuration of the available pixel section 34. The monitor pixel section 35 has dummy pixels used for a correction purpose. The correction circuit 30 is a circuit for correcting a signal received from the monitor pixel section 35 to a proper signal. The correction circuit 30 employs a comparator 31, an output-voltage control circuit 32 and a timing generator 33. The comparator 31 is a section for comparing the signal received from the monitor pixel section 35 with a reference voltage. The output-voltage control circuit 32 is a section for outputting the proper signal mentioned above as a signal controlled on the basis of a comparison result output by the comparator 31. The timing generator 33 is a section for controlling the operations of the comparator 31 and the output-voltage control circuit 32.
In the display apparatus having the configuration described above, first of all, the comparator 31 compares a pixel electric potential VpixH received from the monitor pixel section 35 as an electric potential having the positive polarity with a reference voltage Vref. The comparator 31 is actually a comparator 36 shown in FIG. 18. That is to say, the comparator 36 receives the pixel electric potential VpixH having the positive polarity and the reference voltage Vref, comparing the pixel electric potential VpixH with the reference voltage Vref in accordance with control executed by the timing generator 33. The reference voltage Vref is typically set at 2.85 V. Thus, the comparator 36 compares the pixel electric potential VpixH with the reference voltage Vref in order to determine whether the pixel electric potential VpixH is higher or lower than 2.85 V. Then, the comparator 31 outputs a signal to the output-voltage control circuit 32 as a comparison result indicating that the pixel electric potential VpixH is higher or lower than 2.85 V. On the basis of the signal received from the comparator 31, the output-voltage control circuit 32 outputs a correction signal (or the proper signal mentioned above) to the available pixel section 34 as a signal for generating a proper pixel electric potential. In the display apparatus employing the correction circuit 30 having a configuration described above, the correction circuit 30 finds a proper signal from a signal detected by the monitor pixel section 35 and outputs the proper signal to the available pixel section 34 having a configuration identical with the configuration of the monitor pixel section 35.
It is to be noted that the proper signal output by the correction circuit 30 is also fed back to the monitor pixel section 35 while the operation to drive the display apparatus is being carried out.